WAR Flex .30 cal slugs?

Honestly, buy a NOE bullet sizer and he has many bushing sizes to try relatively cheaply.

First of all you need to size your barrel. Jim at WAR uses TJ's barrels and they are good but can vary 0.0005.

Take your barrel out and oil the inside then GENTLY TAP, using a solid rod or dowel, not a jointed cleaning rod and not steel, a slug that is supposed to be 0.001 larger all the way through, back to muzzle, so it goes through the choke and measure it. Take another slug and tap it in a couple of inches at the rear and back out to see what the true barrel measurement is. Watch out coming back over the port so it doesn't catch and damage your test slug.

A lot of choked barrels shoot a slug sized 0.001 under bore size fairly well. But if you've got a really tight choke you might try a 0.0015 smaller slug but then you might be getting too small for the barrel overall.

Or you could just have Jim make you a slug barrel like I did for both my .25 WARP and my .357 FLEX with no choke and they shoot great!